This invention relates to the beneficiating or concentrating of ores. In particular, this invention relates to collectors useful in ore beneficiating.
Flotation is a process for concentrating minerals from their ores. Flotation processes are well known in the art and are probably the most widely used method for recovering and concentrating minerals from ores. In a flotation process, the ore is typically crushed and wet ground to obtain a pulp. Additives such as flotation or collecting agents and frothing agents are added to the pulp to assist in subsequent flotation steps in separating valuable minerals from the undesired, or gangue, portion of the ore. The flotation or collecting agents can comprise liquids such as oils, other organic compounds, or aqueous solutions. Flotation is accomplished by aerating the pulp to produce froth at the surface. Minerals, which adhere to the bubbles or froth, are skimmed or otherwise removed and the mineral-bearing froth is collected and further processed to obtain the desired minerals.
The basic technique behind froth flotation is to use chemicals to increase the hydrophobicity of the mineral to be beneficiated to form a concentrate. Meanwhile, chemicals are added, as necessary, to decrease the hydrophobicity of unwanted (gangue) minerals, so that these minerals report to the slurry and are discarded as tail. The main alternative technique in froth flotation is “reverse flotation.” This consists of floating the gangue minerals as a concentrate and keeping the mineral of interest in the slurry.
Chemicals that promote hydrophobicity of a mineral are called that mineral's “promoter” or “collector.” Collectors based on fatty acids have long been used in collecting one or more of the oxide minerals such as fluorspar, iron ore, chromite, scheelite, CaCO3, Mg CO3, apatite, or ilmenite.
Also, early work used alkali metal salts of fatty acids, or soaps derived from natural oils by the process known as saponification. When an oil containing triglycerides is treated with a caustic solution under certain harsh processing conditions, the triglycerides disassociate into the alkali metal salts of the component fatty acids. The dissociation of the triglycerides into neutralized fatty acids is the saponification process. These neutralized fatty acids are soaps that act as non-selective flotation collectors.
Compounds containing sulfur, such as xanthates, thionocarbamates, dithiophosphates, and mercaptans, will selectively collect one or more sulfide minerals such as chalcocite, chalcopyrite, galena, or sphalerite. Unfortunately, sulfur based collectors are often toxic, have repugnant odors or both. Amine compounds are used to float KCl from NaCl and for silica flotation. Petroleum-based oily compounds such as diesel fuels, decant oils, and light cycle oils, are often used to float molybdenite. Those oils are also used as an “extender oil” that reduces the dosage of other more expensive collectors in the amine flotation of KCl.
Previous work on sulfide minerals has indicated that molecules containing sulfur are useful compounds for the froth flotation of sulfide minerals. These collectors are usually grouped into two categories: water-soluble and oily (i.e., hydrophobic) collectors. Water-soluble collectors such as xanthates, sodium salts of dithiophosphates, and mercapto benzothiazole have good solubility in water (at least 50 gram per liter) and very little solubility in alkanes. Oily collectors, such as zinc salts of dithiophosphates, thionocarbamates, mercaptans, and ethyl octylsulfide, have negligible solubility in water and generally good solubility in alkanes.
Currently used collectors for most sulfide minerals are sulfur-based chemicals such as xanthates, thionocarbamates, dithiophosphates, or mercaptans. These chemicals have problems with toxicity and/or repugnant odors. In addition, these collectors can be very expensive. Therefore, a need exists for new collectors that are effective but not toxic or odiferous.